This invention relates to mattress foundations and similar devices employing a series of coil support springs, and in particular to an apparatus and process for inserting foam cores into coil springs, the cores being used to increase the firmness of the mattress foundation in the vicinity of the coil having the inserted foam core.
Mattresses, and similar foundations and other structures, are typically composed of a series of longitudinal columns and lateral rows of coil springs which are contained within upper and lower outer border wires. In a mattress, the coils are attached to one another and the outer borders by a series of pigtail wires. Normally, for ease and correctiveness of assembly, the coil springs are identical to one another throughout the mattress foundation, and therefore spring characteristics throughout the mattress foundation are generally identical since the coil springs are the sole support in the mattress.
It has often been desired to increase the firmness in a mattress, for many reasons. In the central area of the mattress, because that area is the primary weight bearing area, it is often desired to strengthen the supporting coils in that area to avoid premature failure of the mattress. In some installations, the peripheral edges of the mattress are often sat upon, and are an area of failure. Strengthening in these areas also leads to longer life of the mattress. In addition, because a mattress will often sag at its edges when weight is applied, additional edge support also provides an increase in the effective usable surface area of the mattress.
Strengthening cores have been applied to springs for added firmness. For example, U.S. Pat. No. 1,936,389 discloses installation of an elastic core to a spring, while U.S. Pat. No. 2,469,596 discloses inserting a foam core in a spring. In either patent, added firmness and increased longevity of the coil springs are the result.
A significant problem inhibiting the use of foam cores in coil springs has been simply the process of physically inserted a core in a spring. Because the foam core normally has a diameter slightly larger than the diameter of the smallest convolution of the spring, it is difficult to force a foam core into a spring, and thus time consuming. Until the present invention, no aid has been available for assisting the ready insertion of foam cores into coil springs. Also, no machine has been known to selectively insert cores into springs only in areas in which increased firmness has been sought.